Elevator safety device.



W. C. STRANG.

ELEVATOR SAFETY DEVICE. APPLICATION FILED JUNE 18, 1912.

1,185,949. Patented June 6,1916.

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APPLICATION FILED JUNE 18, I912- Patented June 6,1916.

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Patented June 6, 1916.

WALTER C. STRANG, 0F YONKERS NEW YORK, ASSIG'NOR TO OTIS ELEVATOR COMPANY, OF YORK, N. Y., A CORPORATION OF NEW JERSEY.

ELEVATOR SAFETY DEVICE.

Specification of Letters Patent.

Patented June 6, 1916.

To all whom it may concern Be it known that I, WALTER C. STRANG, a citizen of the United States, residing at Yonkers, in the county of VVestchester and State of New York, have invented a new and useful Improvement in Elevator Safety Devices, of which the following is a specification.

My invention relates to safety devices or brakes for elevators, and more particularly to that type of car brake in which gripping jaws carried by the car are adapted to grip the stationary vertical guide rails on opposite sides of the car.

An object of the invention is to improve upon the safety devices of this general construction and to control their action in accordance with the load.

Other objects of the invention will appear hereinafter, the novel combinationsof elements being pointed out in the appended claims.

An elevator safety device of the above outlined character, possesses many advantages over all others, but it is defective in one important respect, which is, that as now constructed and installed, it invariably operates the same regardless of the load and speed of the car. That is to say, when the safety device comes into operation the clamping jaws are set up or clamped on the guides with a predetermined pressure. This pressure must be suflicient to retard and stop the car with the heaviest load it may ever be called upon tocarry and it is readily seen that, while the probabilities are that a step will be made under maximum load conditions, the action of the safety device is much too severe for a normal or lightly loaded car. As a 'matter of fact when'the safety device is adjusted to take care of the maximum load, the stop efieoted with a normal or light load is so abrupt that a severe strain is placed upon the mechanism of the elevator, and where passengersare carried, the effect on them is not only ex tremely disagreeable but is frequently the means of causing serious injury. If the safety device be re-adjusted to eflect a stop of the car with a normal load Without discomfort or personal danger to the passengers, the car will not be stopped when a maxlmum load is carried. A

The foregoing points out one of the serious defects of the prevailing type of elevator safety devices, and, with this explanation, I

will now proceed to describe an elevator safety device containing an embodiment of my invention which is designed to overcome the defects and objectionable features inherent to this class of apparatus in a simple, practical and efficient manner.-

Referring to the drawings, Figure 1 is an elevational view of an elevator containing an embodiment of my invention; Fig. 2 is a plan view of the bottom of the elevator car showing the safety device; Fig. 3 is an enlarged sectional detail view of a dashpot;

Fig. 4 is a sectional side view of the safety device; Fig.5 is a plan View of Fig. i; Fig. 6 is a modification; Fig. 7 is an end sectional view of Fig. 6 taken on the line a-a; Fig. 8 isa fragmentary sectional plan view of Fig. 6; Fig. 9 is a sectional plan view-of a further modification; Fig. 10 is a sectional end view of Fig. 9 on the line b-b.

Like reference charactersdenote similar parts throughout the various. figures.

In the drawings, Fig. 1 illustrates suf- V I ficient of an elevator apparatus to show one means of. carrying out my invention. An elevator car C is suspended from the usual cables 1 which-may be connected with the usual counterbalance weight and any de-. sired form of hoisting engine, such as an electric motor to effect the operation of the elevator. A governor cable 2 is yieldingly secured to the car, by means of a releasing carrier 3, and under normal conditions travelsat the samespeed as that of the car. The governor cable passes over the sheave of the governor 4 at'the top of the hatchway and is subjected to a light tension by means of a weighted pulley 7. adapted to havea certain small movement in a stationary frame 8 secured at the bottom of the hatchpulleys 10 and wound about the safety drum. The governor 4 is provided with cable clamps 5 which operate to grasp the governor cable with a yielding pressure whenever the speed of the car becomes excessive or exceeds a certain predetermined amount. The safety device comprises the safety drum 12 (see Figs. 2, 4 and 5) provided with hubs at either end which are carried in bearings '13, 13, securely bolted to the channel beams 11, the arrangement being such that the drum may have a small axial movement inthe bearings 13, 13. The drum 12 is connected to the two pairs of toggles 14, 14, through the medium of shafts 15, 15, each of which is reversely threaded at opposite ends, one end extending into the threaded socket of a box 16, connected with the toggle 14, and the other into a threaded socket of the box 17 upon a threaded shaft 18 which is screwed into the hub of the safety drum. The toggles 14 are connected to the ends of pairs of gripping jaws or clamps 19 which are adapted to' be applied to the guide rails 20 upon opposite sides of the car. While I have shown a toggle connection between the boxes 16 and the clamping jaws, it is obvious that various other mechanical devices could just as well be used, such as wedges or cams.

' So far as the general arrangement above described is concerned, the construction and operation do not materially differ from that set forth in the patent to A. O. Ellithorpe, No. 376,374, dated January 10, 1888. As in the apparatus disclosed in the Ellithorpe patent, any undue speed of the cage will throw .out the governor balls, arrest the movement of the governor table 2, and drawing upon the cable 9 will rotate the drum 12 and screw outwardly the shafts 18 and apply the clamps to the guides to retard or stop the car. In the present construction, however, the arrangement of the shafts 15 and their reversely threaded ends and the boxes 16 and 17 is different than that shown in the Ellithorpe patent, so that each shaft 15 is so mounted that it can be turned independently upon its axis whether the drum 12 is in motion or not, and the rotation of the shafts with the reverse threads at the opposite ends will serve as a means of separating or bringing together the boxes 16 and of applying or loosening the clamping jaws. Preferably both shafts 15, 15, should be turned simultaneously, and to this end I provide each shaft 15 with an arm 21 se curely fastened thereto and connected by a rod 22 with anarm 23 secured to a shaft 24 suspended below the bottom of the car by a pair of brackets 25. It will be noted that while the rotation of the drum 12 will force apart the shafts 15' and their connected arms 21 tending to cramp the rods 22, sufiicient side play in the connections of these rods is provided so as to avoid this, the outward movement of the shafts 15 be ing of small amount under all conditions.

From the foregoing it is seen that a rotation of the shaft 24 acting through the medium of the threaded shafts 15 will effect an application or release of the clamping jaws independently of the operation of the safety drum 12, and in the preferred embodiment of my invention, I propose to effect the control of the safety device by utilizing this shaft as an intermediate mechanism.

Referring more particularly to Figs. 1 and 2, I have shown an arm or lever 26 carrying an adjustable weight 28 secured to the shaft 24. Intermediate the ends of the lever 26 is connected the piston rod of a dashpot 27 Which is pivotally connected to.

the bottom of the car by means of a bracket 29. A spring 30 (see Fig. 3) surrounds the dashpot piston rod and tends to move the latter upwardly against the action of the weight 28, the tension of the spring being such that the lever 26 will float or assume the position shown in Fig. 1, in which it is capable of a movement in either direction. The piston 31 has an air tight sliding fit with the inside of the dashpot and is provided with a port which is normally closed by a swinging check valve 32. A port 34 communicates with the interior of the dashpot chamber and this port may be restricted any desired amount bymeans of an adjusting plug or screw 33.

The operation of the apparatus thus far described may be seen from the following: Assuming the elevator car to have attained an excessive speed over and above that for which the centrifugal governor was set, the

latter at once operates the cable clamps 5 which grip and hold stationary the governor cable 2. A continued movement of the car releases the cable from the car at the releasing carrier 3 and the safety cable 9 effects a rotation of the safety drum 12. As the latter rotates, the threaded shafts 18, 18, are moved outwardly, thereby operating the toggles 14 to effect the clamping of the jaws on the guide rails to retard or 1 which, as before pointed out are yielding,

and whose clamping pressure or grip is regulated by means of a spring. It is de sirable that the governor cables be permitted to slip through the clamps 5 with this type of safety device, otherwise the strain on the governor or safety cables would become excessive if the car should fail 'to stop within a certain distance.

In order to insure the stoppage of the car with a maximum load in the car, the cable clamps 5 are adjusted to effect a powerful braking action by the clamping jaws 19. If the rate of retardation of the car is within practical bounds so as not to discomfort the passengers, the momentum of the weighted lever 26 is so gradually overcome, that the latter will have practically no movement relatively to that of the car and hence it will not interfere with the retardation or braking of the car. If, however, the car be normally or lightly loaded, the normal action of the clamping jaws will tend to be entirely too severe, hence under the usual conditions the rate of retardation of the car will become excessive. As soon as the rate of retardation tends to become too rapid, the momentum of the weighted lever 26 overcomes the opposing tendency of the spring 30 and the lever moves downwardly with respect to the car thereby rotating the shaft 24 and connected shafts 15, 15 in a direction to relieve the pressure of the clamping jaws on the guide rails. The rate of retardation is now reduced to such an amount that the weighted lever no longer tends to relieve the braking pressure and the continued pull on the safety cable tends to increase the rate of retardation which tendency will again be opposed by the action of the weighted lever 26.

It will be observed that the braking action upon the car is controlled by two factors; the one, tending to effect a rapidrate of retardation under normal load conditions, while the other tends to oppose the action of the first named factor. This opposing action may be effective or it may not, depending upon the rate of retardation of the car, which in turn is dependent upon the load. The resultant action of the factors upon the safety device is to give a smooth gradual braking action upon the car under all pos sible conditions of load and speed. While the above description of the action of the safety device might lead one to suppose that the operation of the same will be intermit tent, as a matter of fact this will not be so, since the instant the car tends to effect too quick a stop the weighted lever immediately acts to offset or compensate for this tendency and the resultant brake action will be uniform and smooth, without any tendency to effect violent speed changes and shocks. The weighted lever will act as a governor or controlling device for checking or reducing the action of the safety drum and its connections upon the clamping jaws, hence the weighted lever and its connections may be considered as a momentum governor which is responsive to load conditions and through its action upon the safety device renders the latter as a whole responsive to load conditions and under the control thereof. It will be observed that after the safety device has operated and the car has substantially come to rest, if the load. has been less than a maximum load and the lever 26 has moved downwardly to control the retardation of the car, thespring 30 will be compressed and will exert a greater pressure upon the lever 26 than it did before the'safety device came into action. The pressure of the spring is such at this time that it overpowers the action of gravity on the weight 28 and tends to move the lever upwardly and increase the pressure of the clamping jaws upon the guide rails. The action of the clamping jaws under these conditions is first to exert an initial and powerful brake action; then this brake action is reduced in proportion to the load, and then again increasedto a greater degree than when first applied. This mode of operation of an elevator safety device or brake is most desirable and eflicient and tends to effect a smooth gradual stop of the car and to clamp the latter firmly to the guides and thereby prevent any possibility of the car continuing to the bottom of the shaft. In order that the momentum governor may itself be constructed and regulated. so as best to perform its functions, I have provided several adjustments. The weight 28 may be moved along the lever 26 and secured in the most favorableposition thereon, the lever itself may be of any desired length, while theopposing spring 30 may be located at various points along the lever and have its tension varied by any suitable means such as the nut shown directly above it. The dashpot 27 may or may not be used as desired, and when used is provided with means for retarding'the upward movement of the weighted lever, which means may be regulated to secure the best results. While the dashpot as shown, permits a free movement of the weighted lever sired degree, and by slightly altering the dashpot, the same may-be utilized to retard the movei'nent of the lever 26 in either or both directions. The spring 30 and dashpot 27 may be incorporated in a single structure as I have shown in Fig. 3, or they may be separated and applied to different parts of the lever device.

Inasmuch as the actionof a safety device containing an embodiment of my invention is responsive to and controlled by the load on the car,'it will be seen that the operation of the device will tend to stop the ear in a predetermined distance regardless of the load conditions. The fly-ball governor effects the initial operation of the safety at a predetermined car speed of so many feet.

per minute, and the subsequent operation of the device is in accordance with the load, hence the car will tend finally to come to rest after having traversed a certain predetermined distance, which distance will be uniform for all loads. This feature is of great practical value, both from a mechanical standpoint and by reason of the fact that the minimum distance through which a human body traveling at a certain speed can be brought to rest is well defined, and cannot be lessened without discomfort or danger to the passengers.

It sometimes happens that a safety device may be operated when the car is only a short distance away from its lower limit of travel and, owing to the limited distance through which the car has to move before it bottoms or reaches the lower end of its run, the safety device will not have sufficient time to bring the car to rest. Under these conditions the car will bring up at the bottom of the hatchway with a crash which of course is most undesirable and is certain to have dire results both to the elevator apparatus and the passengers in the car. In order to overcome this contingency I provide at or near the lower end of the elevator run a stationary cam 35 (see Fig. 1) which is adapted to engage some part of the safety device, preferably the lever 26. Should the safety device operate while the car is but a short distance from the bottom, the cam 85 will engage the lever 26 to move the latter upwardly with respect to the car and apply the safety clamps to the guide rails with maximum pressure which pressure may be considerably in excess of the normal pressure set up by the action of the governor cable and its connections. The result of this action will be to bring the car to a positive stop before the latter shall reach the bottom of the hatchway. \Vhile this stop may be rather more abrupt than is consistent with the comfort of the passengers, it will prevent actual damage both to the elevator mechanism and to the passengers. This cam may be so arranged as to effect the operation of the safety clamps even though the governor has not operated the safety device, since any substantial movement of the lever 26 in an upward direction tends to rotate the re versely threaded shafts 15, 15, in a direction to apply the clamping jaws to the guides.

Turning now to Figs. 9 and 10, I showv a modification of my invention, which, while utilizing substantially the same principle of operation, that is to say, a load controlled safety device, the method of applying this principle differs somewhat from that already disclosed in connection with the other figures. The safety device here shown is substantially like those in common usage comprising the usual safety drum 12 and right and left screws connected to the drum with a friction'or brake surface 36,

which co-acts with a band or other suitable friction brake 37, which is normally out of contact therewith. This friction band is secured at either end to the weighted lever 26 in such manner that a downward movement of the latter will tend to apply a braking action to the drum and thereby retard or preventits rotation. The lever, as before, may be, and preferably is, provided with a dashpot 27, which is connected to the same by means of an extension bracket 38, the spring 30 being situated in this case on the opposite side of the pivot of the lever. A handle 39 is secured to the lever and extends through the floor of the car so as to permit an occupant therein to manipulate the brake if occasion demands.

The operation of the device just described may be seen from the following: Assuming the safety device to have operated by the governor in the usual way, the drum 12 will rotate and tend to force the wedges 4:1, 11, between the ends of the clamping jaw le vers to apply the jaws with maximum pressure upon the guide rails. the car be a maximum load, the braking pressure of the gripping jaws will be sufficient to retard and stop the car in the proper distance and without shock or jar to the passengers. If, however, the load be other than a maximum load, say. a light load, the rapidly increasing pressure of the clamping jaws on the guides will soon reach a point at which the rate of retardation of the car will tend to become excessive. Before this rate has had time to become excessive, its influence is felt by the weighted lever 26, and the latter will move downwardly and apply the friction brake 37 to the drum. The resistance of the drum to turning has now become such that the governor cable is pulled through the governor clamps at the top of the hatchway, and the safety de vice is not applied with the same pressure on the guides as in the case of a maximum load without-the opposing action due to the weighted lever or momentum governor. Thus it will be seen that no matter what the load on the car may be, the action of the safety device will be controlled by the load through the instrumentality of the momentum governor, which as .pointed out, is responsive to changes in speed. The function of the dashpot is substantially the same as before in that it controls the motion of the weighted lever 26 to a greater or less extent as desired to effect the best results. In order to reset the safety device after the same has operated, I may provide an arrangement similar to that shown in Figs. 2, 4 and 5, which comprises a bevel gear formeddn one end of the safety drum by If the load in means of which the drum may be rotated backward from withinthe car.

Figs. 6, 7 and 8, represent a further modification of my invention, in which the safety drum 12 is provided with a long hub 42 which is carried upon a shaft 43 supported in bearings 45, 45, and free to rotate on said shaft, collars 44, 44, upon the shaft preventing a longitudinal -movement thereof. The opposite ends of the shaft 43 are reversely threaded at 47, 47, into cam or wedge members 48 adapted to wedge the gripping jaws upon the" guide rails when the shaft 43 is rotated. In order to effect the rotation of this shaft from the drum, I provide a series of friction disks, such as 52 and 53, of which any desired number may be used, each alternate disk as 52 being keyed to the shaft but having a longitudinal movement thereon, while the intermediate disks such as 53 are free to turn with respect to the shaft, but are positively driven by the drum by means of the projections 46, 46, which enter slots in each disk. 53. It is evident from this construction that a rotary motion of the drum will tend to rotate the shaft 43 through the medium of the friction disks 52 and 53. In order that there shall be suflicient friction between these disks to effect the desired result, I provide a spring 57, whose tension may be regulated by means of the adjusting nuts 58 and which bears against 'a thrust collar 54 in contact with one of the disks 52. The pressure of this spring will be transmitted throughout the disks and the amount of this pressure acting through the friction, surfaces of the disks will determine the amount of power that thedrum can transmit to the shaft 43 and through it to the clamping jaws. The thrust collar 54 is keyed to the shaft 43 and has bevel gear teeth out on one end, and is provided with acircumferential groove 55 in which lies a pair of pins 56 carried upon the bifurcated ends of a bell crank 55. This bell crank is pivoted to a standard 50 and one end 26 extends horizontally under the floor of the car and carries upon it an adjustable weight 28.

The operation of the device just described is as follows: As soon as the governor operates to grip the governor cable, the drum 12 will rotate and a rotary motion will be transmitted from the drum to the disks 53 and by friction to the disks 52,

. sengers.

cation of the brake. As before, the action of the Weighted lever 26 or momentum governor, is responsive to load conditions, and

by automatically varying the pressure on the disks, will permit and enable the clamping jaws to effect a retardation of the car, which will be responsive to load conditions.

The primary object of the rod 59 is to facilitate the resetting of the safety device after the same has operated. To do this it is merely necessary to press downwardly uponv this rod, thereby moving the thrust collar into engagement with the bevel pinion 60 and removing the spring tension from the disks, whereupon, by turning the pinion 60 the shaft 43 is positively rotated through the thrust collar 54, and the gripping jaws are withdrawn from the guide rails.

vFrom the foregoing, it is seen that a safety device embodying my invention is extremely simple and free from complicacations, is very practical, while at the same time it can easily be applied to safety de-' vices already in use with practically no changes in the mechanism whatever. The device is efficient, since it is responsive to and acts in proportion to the load, which it is required to retard and bring to a stop. Furthermore a satisfactory stop can be made under any and all load conditions without shock or jar to apparatus or pas- The device lends itself to many and various types of elevator safeties, and it is shown and described in connection with the Ellithorpe clamp jaw safety, since that particular type of elevator safety has proven to be one of the most effective constructions now in practical use. I -I have shown several modifications of this invention, to show that it is not limited to any specific construction. My invention may be applied to many of the forms of elevator safety devices which are lmown in the art, and I do not wish to limit myself in any way to the particular forms of safety devices which I have shown and described to illustrate the operation, nor do I wish to be limited to the particular arrangement of parts comprising the invention as disclosed, since various changes could readily be made by one skilled in the art, without departing from the spirit or scopeof the invention. s

' I believe it is broadly new to effect the application of a safety device in accordance with the load and automatically to bring about the. retardation and stop of an elevator car at any point in its travel, within a predetermined distance, regardless of load conditions.

What I claim is 1. The combination with an elevator safety brake, of means controlled by speed for effecting the retardation thereof in accordance with the load.

2. The, combination with safety brake, of automatic speed controlled means for effecting the retardation thereof in accordance with the load.

3. The combination with an elevator safety brake, of automatic means for efiecting the operation thereof, and load controlled means for controlling the said automatic means. 4

4. An elevator car, a safety device adapted to retard the car, and a governor for controlling the rate of retardation in accordance with the load.

5. An elevator car, a safety device therefor and a momentum governor for controlling said safety device in accordance with the load.

6. An elevator car, a brake therefor, a centrifugal governor for effectingthe application of said brake, and a momentum governor for controlling said brake.

7. An elevator car, means for retarding said car, and speed controlled means for automatically varying the rate of retardation in accordance with the load.

8. An elevator car, means for retarding said car upon excessive car speed, and means for controlling the rate of retardation in proportion to the load.

9. An elevator car, mechanical means for retarding said car, and means responsive to the rate of retardation for controlling said retarding means.

10. An elevator ca r, mechanical means for retarding said car, and a momentum governor forcontrolling the rate of retardation.

11. An elevator car, speed controlled means for effecting a retardation of said car, andmeans for controlling said retarding means in accordance with the load.

12. An elevator car, speed controlled means for effecting a retardation of said 'car, and automatic means controlled by the load for controlling said retarding means. 13. An elevator car, means for effecting a predetermined brake action to stop the car, and means for controlling said brake action in proportion to the rate of retardation.

14:. An elevator car, means for effecting a predetermined brake action gradually to stop the car, and means responsive to load conditions for controlling the said brake action. 15. An elevator car, means for applyinga brake to stop the car, and means for opposing the action of said brake With a variable power. I

' 16. An elevator car, means for applying a brake to stop the car, and automatically an elevator operated means for opposing the action of said brake with variable power.

17 An elevator car, means for applying a brake to stop the car, and means for oppose ing the action of said brake in accordance with the load.

18. An elevator car, a safety brake device therefor, means for applying said brake with maximum power, and automatic means for easing ofi' said brake during the application thereof.

. 19. An elevator car, a safety brake device therefor, means for applying said brake with maximum power in the event of the car attaining excessive speed, and automatic load controlled means for reducing the brake action.

20. An elevator car, a safety brake therefor, means for applying said brake wltn maximum power in the event of excessive car speed, and automatic means for limiting the power of said brake in accordance with the load on the car.

21. An elevator car, a safety brake therefor, speed controlled means for applying said brake with. maximum power, and automatic means controlled by the rate of retardation ofthe car for reducing the power of said brake.

22. An elevator car, a safety brake therefor, and means operative upon excessive speed for applying said brake gradually to stop the car in a predetermined distance regardless of the load in the car.

23. An elevator car, a safety brake therefor, and means operative upon excessive speed for gradually applying said brake to stop the car in a predetermined distance regardless of the load.

24. An elevator car, a safetybrake there for, and automatic speed controlled means for applying said brake gradually to stop the car in a predetermined distance with varying loads.

25. An elevator car, a safety brake therefor, and automatic means controlledby the load and speed for applying said brake gradually to stop the car in a predetermined distance regardless of-load conditions.

26. An elevator car, means for applying a brake to stop the car, and means controlled by the rate of retardation in stopping for preventing a too sudden stop'of said car.

27 An elevator car, a safety brake'there- .for, and meanscontrolled by the action of said brake for preventing a too sudden stop of the car.

28 Anelevator car, a brake therefor, and centrifugal and momentum' governors for controlling said brake;

29. An elevator car,a safety brake therefor, a centrifugal governor for effecting the initial operation'of saidsafety brake, and an additional governor for controlling said brake." T

and operatively connected to said device,

and load controlled means for controlling the movement of said lever.

33. An elevator car, a safety brake therefor, means for varying the power of said brake and automatic means for controlling said power varying means.

34. An elevator car, a safety device therefor, a momentum governor for controlling said device, and means for retarding theaction of said governor.

35. An elevator car, guides. over which the car travels, a clamping device carried by said car and adapted to effect an engagement with said guides to stop the car, means for efl'ecting the operation of said device,

and means controlled by the load on the car for efi'ecting a partial release of said device. 1

36. An elevator car, guides therefor, a clamping device on the car adapted to engage said guides, speed controlled mechanism for modifying the operation of said clamping device.

37. An elevator car, a safety device therefor, means for effecting the operation of said device, means responsive to changes in speed for controlling said device, and a dashpot for controlling said controlling means.

38. An elevator car, a safety brake therefor, means for effecting the application of said-brake to retard and stop the car, a weighted lever pivoted to the car, a spring acting in opposition to said lever, and an operative connection between said lever and said safety brake, for the purpose set forth.

In an elevator, the combination of a safety device and means for operating the same, a governor for controlling the said device, said governor comprising a pivoted lever carried on the car, a weight for moving said lever, and a spring opposing the action of said weight.

40. An elevator car, a safety device therefor, means for applying said device, means comprising a floating weight acting in opposition to said applying means, and means for retarding the movement of said weight.

4L1. An elevator car, a safety brake therefor, means for effecting the normal complete application of said brake, and automatic means for increasing the power of said brake.

42. An elevator car, a safety brake therefor, speed controlled mechanism for effecting the application of said brake with normal power, and means for increasing the power of said brake at a predetermined point in the travel of the car.

4L3. An elevator car, a safety device therefor, speed controlled means for operating said device, and independent means for effecting the operation of said device at a predetermined point in the car travel.

44. An elevator car, a safety clamp on said car adapted to engage a stationary element in the hatchway, and load controlled differential actuating mechanism for effect ing the application of said clamp in accordance with the load I 45. An elevator car, a safety device therefor, means for operating said device, and means for retarding the said operating means in accordance'with the load on the car 46. An elevator car, safety clamps on the In testimony whereof, I have signed my 4 name to this specification in the presence of two subscrlbing witnesses.

WALTER 0. strains.

Witnesses:

ERNEST L. GALE, Jr., JAMES G. BETHELL.

Copies of this patent may be obtained for five cents each, by addressing the Commissioner of Patents, Washington, D. 0. 

